1. Field of the Invention
The present invention relates to a high pressure fuel injection pipe disposed in such a manner as to connect to nozzle holders respectively arranged near a cylinder head and near a fuel pump for a fuel supply passage in a diesel engine and having a relatively narrow pipe diameter equal to or less than 20 mm, and to a method of manufacturing the same.
2.Description of the Prior Arts
Conventionally, as this kind of high pressure fuel injection pipe for a diesel engine, Japanese Patent Examined Publication No. 1-46712 belonged to the applicant of this application has been known. The high pressure fuel injection pipe described in this publication is structured such that a double metal pipe is constituted by press-fitting a thin internal pipe made by a stainless steel pipe and having a communication passage formed therein into an external pipe made by a thick steel pipe, and a thickness of the internal pipe is set to be 1.2 to 8.5% of an outer diameter of whole of the double metal pipe.
Then, the high pressure fuel injection pipe described in this publication can prevent a cavitation, erosion and corrosion (hereinafter, refer to a cavitation) from generating on an inner peripheral surface even when the high pressure fuel injection pipe is operated under a recent condition for increasing a fuel injection pressure as a measure for reducing NOx and a black smoke of 1 to 2 mile second of an injection time, 50 m/sec of a maximum flow speed and 600 to 1000 bar (a peak pressure) of an internal pressure, and can substantially satisfy a durability against a repeated high pressure fatigue.
However, a trend of increasing a pressure of a fuel has been further significant, and it is expected that a high pressure fuel injection pipe which can obtain a performance of standing against the cavitation even in a condition of 800 to 1400 bar (a peak pressure) of an internal pressure is provided. Accordingly, there is a possibility that the injection pipe described in the above publication can not sufficiently operate an anti-cavitation performance in this high pressure condition.
Further, there is a problem that at a time of forming a connection head portion of an injection pipe material constituted by a double metal pipe, a formation is hard since a work hardening together with forming an extension pipe is generated in the injection pipe material.